JP2018169220A - Laminated body - Google Patents

Abstract

To provide a laminated body that can obtain an oxidation current sufficient for determining the concentration of a substrate even at a low voltage and can obtain a measurement result with the noise current suppressed, and also can attain a high electrochemical activity and a high conductivity at the same time.SOLUTION: In a laminated body 101, an undercoat layer 104 is formed on a base material 103 made of a high-molecular compound, and a conductive layer 105, in which a carbon nano-tube is dispersed using an ionic polymer material as a dispersant, is laminated on the undercoat layer. When the laminated body is used as an electrode, the electric charge movement resistance rate at the self-potential is 2.0×10Ωcmor smaller.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a laminate having, on a base material, a conductive layer containing carbon nanotubes having both high electrochemical activity and conductivity and a carbon nanotube dispersant.

  There has been proposed a biosensor capable of easily quantifying a specific component present in a biological sample or the like without diluting or stirring the sample. As an example, Patent Document 1 discloses that an electrode and an electrode wiring are formed by performing wide-area electric field laser removal after performing metal sputtering on an insulating substrate, and contains an enzyme and a redox substance on this electrode. A biosensor having a reagent layer is disclosed. This biosensor quantifies the substrate concentration in a sample as follows.

  First, by dropping the sample solution onto the reagent layer of the biosensor, the reagent layer is dissolved, and an enzyme reaction proceeds between the substrate in the sample solution and the enzyme in the reagent layer. Accompanying this enzymatic reaction, the redox form is reduced. After a certain time, a constant voltage is applied to the sensor electrode to electrochemically oxidize the reduced redox substance, and the oxidation current value obtained at this time is measured. Since this current value is directly proportional to the substrate concentration, the substrate concentration in the sample solution can be quantified. Such a biosensor has already been put to practical use as a sensor for measuring glucose concentration in blood.

  In order to perform highly reproducible measurement, it is necessary to suppress the noise current caused by the reaction of contaminants in the sample solution. As a means to suppress the reaction with contaminants, there is a method in which oxidation of the redox substance is performed at a lower voltage, but in order to obtain an oxidation current value sufficient for quantification of the substrate concentration at a low voltage, the electrode is redox. Preferably have good electrochemical activity.

  In order to keep the applied voltage constant, it is necessary to consider the influence of the voltage drop due to the wiring resistance of the electrode formed by the conductive layer. It is assumed that the wiring resistance varies depending on the manufacturing lot and the external environment, but the higher the conductivity of the conductive layer, the smaller the voltage drop amount, and relatively less variation in wiring resistance, that is, variation in applied voltage. Therefore, the conductive layer preferably has high conductivity.

  In addition, it is important to always keep the electrode area constant in order to perform highly reproducible measurement. As a typical method of forming a uniform electrode, there is a method of performing laser etching on a conductive layer formed on a substrate. However, uniform laser etching is possible by suppressing the occurrence of burrs and short circuits during etching. As a premise, the conductive layer needs to be a thin film.

  Carbon nanotubes are attracting attention as materials having good electrochemical activity and high conductivity potential. For example, Patent Literatures 2 to 4 report biosensor electrodes using carbon nanotubes.

JP 2011-203268 A Japanese Unexamined Patent Publication No. 2016-212067 JP 2005-172770 A Special table 2012-511714 gazette

  However, in Patent Document 2, multi-walled carbon nanotubes having a diameter of 100 nm or more are used as carbon nanotubes, and electrochemical activity and conductivity are compared with single-walled and double-walled carbon nanotubes having a small diameter and a small number of layers in terms of the thickness. Sex was not enough.

  Patent Document 3 proposes an electrode having a structure in which carbon nanotubes are sealed with an insulator and a part of the carbon nanotubes is exposed from the insulator. However, a sample solution enters the carbon nanotube portion sealed with the insulator. In other words, the electrochemical activity was not sufficient because an electrochemical reaction could not occur.

  In Patent Document 4, a carbon nanotube conductive layer is formed without a carbon nanotube dispersant, but carbon nanotubes are usually hydrophobic and have low electrochemical activity due to low affinity with the sample solution. In order to enhance the electrochemical activity, a method of depositing metal particles as catalyst nanoparticles has also been proposed, but metal particles generate more noise due to background current than carbon nanotubes. Not suitable for use with biosensors to measure.

  As described above, it is known that the characteristics of carbon nanotubes vary greatly depending on many factors such as the number of layers, the external environment, and purity. The electrochemical activity is a reaction at the interface between the electrode and the sample solution, and is extremely sensitive to the surface state of the carbon nanotube. In general, the condition of carbon nanotubes with high conductivity is high purity, but the surface of carbon nanotubes with high purity has low electrochemical activity, and there is a trade-off between conductivity and electrochemical activity. It was a relationship.

The present invention has the following features in order to solve such problems. That is,
(1) A laminate having a carbon nanotube and a conductive layer containing a carbon nanotube dispersant on a substrate, potassium ferrocyanide at a concentration of 5 mmol / l, potassium ferricyanide at a concentration of 5 mmol / l, and 0.5 mol / l A laminate having a charge transfer resistivity at a natural potential of 2.0 × 10 ⁻⁹ Ωcm ³ or less on the basis of a silver / silver chloride electrode when immersed in an aqueous solution containing potassium chloride at a concentration of 5%.
(2) The laminate according to (1), wherein the electric resistivity of the conductive layer is 5.0 × 10 ⁻⁴ Ωcm or less.
(3) When the entire conductive layer is 100% by mass, the following first carbon nanotubes are contained in an amount of 1.0% by mass or more and the second carbon nanotubes are contained in an amount of 1.0% by mass or more ( The laminate according to 1) or (2).
First carbon nanotube: by resonance Raman scattering measurement, the maximum peak intensity in the range of 1,560~1,600cm ^-1 G, a maximum peak intensity in the range of 1,310～1,350Cm ^-1 A second carbon nanotube having a G / D of 30 or more when D is D: the G / D is 10 or less (4) The carbon nanotube includes a double-walled carbon nanotube (1) to (3) The laminated body in any one of.
(5) The laminate according to any one of (1) to (4), wherein the carbon nanotube dispersant contains carboxymethylcellulose.
(6) An electrode sensor comprising the laminate according to any one of (1) to (5).

  According to the present invention, it is possible to provide a laminate having high electrochemical activity and conductivity.

It is a conceptual diagram of the cross section of the laminated body which has a conductive layer on a base material. It is a conceptual diagram of a carbon defect. It is a conceptual diagram of a double-walled carbon nanotube. It is a conceptual diagram of blood glucose level sensor wiring. It is a conceptual diagram of an equivalent circuit.

  Hereinafter, embodiments of the laminate will be described.

[Base material]
The substrate used in the present invention is preferably a polymer compound in order to achieve the purpose of mass production at low cost, but is not particularly limited, and glass, quartz, sapphire, silicon, metal, etc. You can choose from a wide range. Examples of the polymer compound include polyester, polyolefin, polyamide, polyesteramide, polyether, polyimide, polyamideimide, polystyrene, polycarbonate, poly-ρ-phenylene sulfide, polyether ester, polyvinyl chloride, polyvinyl alcohol, poly ( Examples thereof include (meth) acrylic acid ester, acetate type, polylactic acid type, fluorine type, and silicone type. Further, these copolymers, blends, and further crosslinked compounds can be used.

  Further, among the above-mentioned polymer compounds, those composed of polyester, polyimide, polystyrene, polycarbonate, poly-ρ-phenylene sulfide, poly (meth) acrylic acid ester, etc. are preferable, and comprehensive consideration is given to workability and economy. Then, a synthetic resin made of polyester, particularly polyethylene terephthalate is preferably used. These base materials may be subjected to various pretreatments such as UV ozone treatment and lamination of an undercoat layer as long as the spirit of the invention is not impaired.

  In addition, if a base material is a film, since a flexible laminated body can be obtained and it can be used for the curved surface part of an electronic device, or it can be used for the electronic component which needs a bending, it is preferable. Furthermore, it is preferable to use a film wound in a roll shape because it leads to continuous production of the laminate of the present invention by roll-to-roll, and there is a merit in terms of cost. In particular, it is preferable to use a polyester film as the film.

  Moreover, when using as a blood glucose level sensor, in order to improve the visibility of blood, it is preferable to use a white base material. White refers to a color defined by JIS L1015 (2010), which is defined by whiteness measured by the Hunter method, and exhibits a value of at least 70%, preferably 90% or more. The thickness of the substrate is preferably in the range of 1 μm to 500 μm, more preferably in the range of 30 μm to 300 μm, and still more preferably in the range of 50 μm to 250 μm from the viewpoints of handling and flexibility.

[Surface hydrophilization]
In the present invention, as described later, it is preferable to apply a coating composition containing an aqueous solvent (hereinafter sometimes referred to as an aqueous undercoat solution) onto a substrate. In order to improve the coatability (coating without repelling) of the water-based undercoat solution, physical treatment such as corona treatment, plasma treatment, flame treatment, etc. as chemical methods such as corona treatment, plasma treatment, flame treatment, etc. It is preferable to carry out an automatic treatment. Of these, corona treatment and plasma treatment are preferred. These treatments are preferable because, for example, the water contact angle on the substrate surface can be set to 5 ° or more and 55 ° or less, and the aqueous undercoat liquid can be efficiently applied to the substrate.

[Undercoat layer]
In order to improve the coating property of the carbon nanotube dispersion liquid described later on the base material and to improve the adhesion between the conductive layer containing carbon nanotubes and the base material, it is preferable to provide an undercoat layer on the base material. The undercoat layer preferably contains an organic binder and particles. Details of the undercoat layer will be described below.

<Wetting tension, thickness and roughness of undercoat layer>
The undercoat layer preferably has a wetting tension of 76 mN / m or more and 105 mN / m or less as defined by ISO 8296 (2003). By setting the wetting tension to 76 mN / m or more, it is preferable that when the carbon nanotube dispersion liquid is applied on the undercoat layer, it is difficult to repel the coating and the carbon nanotube dispersion liquid can be uniformly applied. . Also, if the wetting tension of the undercoat layer is 105 mN / m or less, coating unevenness due to spreading of the coating liquid during coating and coating unevenness affected by wind during drying are less likely to occur, and the carbon nanotube dispersion liquid It is preferable because it can be applied uniformly. From the viewpoint of uneven coating, the wetting tension is preferably 76 mN / m or more and 105 mN / m or less, and more preferably 76 mN / m or more and 90 mN / m or less.

  The wetting tension of the undercoat layer can be increased by increasing the copolymerization amount of the hydrophilic functional group contained in the organic binder in the coating composition forming the undercoat layer or by increasing the thickness of the undercoat layer. Can be bigger. Therefore, the wetting tension of the undercoat layer can be appropriately adjusted depending on the copolymerization amount of the hydrophilic functional group contained in the organic binder, the type of the hydrophilic functional group, and the thickness of the undercoat layer.

  The thickness of the undercoat layer can be arbitrarily set as long as a phenomenon such as curling hardly occurs when the laminate is formed and the wettability of the surface of the undercoat layer is within the preferable wet tension range.

<Organic binder>
In order to improve the adhesion between the conductive layer containing carbon nanotubes and the carbon nanotube dispersant and the substrate, the undercoat layer preferably contains an organic binder. As the composition of the organic binder, for example, phenol, silicon, nylon, polyethylene, polyester, olefin, vinyl, acrylic, cellulose and the like are preferable.

  The organic binder is preferably an organic binder having a hydrophilic functional group from the viewpoint of applicability to a substrate. The organic binder is more preferably a polyester resin having a hydrophilic functional group and / or an acrylic resin having a hydrophilic functional group from the viewpoint of applicability to a substrate. That is, the organic binder may be either a polyester resin having a hydrophilic functional group or an acrylic resin having a hydrophilic functional group, or a polyester resin having a hydrophilic functional group and an acrylic resin having a hydrophilic functional group. Both may be, but both polyester resin having a hydrophilic functional group and acrylic resin having a hydrophilic functional group can improve adhesion to the substrate and improve the coating properties of the carbon nanotube aqueous dispersion. It is preferable from the viewpoint.

<Particle>
In the present invention, the undercoat layer preferably contains particles. By including the particles, the coating property of the carbon nanotube dispersion liquid can be further improved. Moreover, since antiblocking property can also be provided to an undercoat layer, it is preferable. That is, when producing a laminate by roll-to-roll, it may be necessary to wind up the substrate on which the undercoat layer is formed after the undercoat layer is formed, and in that case, by including particles in the undercoat layer, Since an undercoat layer becomes difficult to block, it is preferable.

  The content of the particles is preferably 5% by mass or more and 95% by mass or less when the entire undercoat layer is 100% by mass. When it is less than 5% by mass, the surface of the undercoat layer is insufficiently uneven, and the anti-blocking property may not be exhibited. On the other hand, if it exceeds 95% by mass, the particles may be excessive with respect to the binder, and the particles may fall off. A preferable range of the particle diameter is 5 nm to 500 nm. More preferably, they are 15 nm-100 nm, More preferably, they are 15 nm-40 nm. In addition, a particle diameter here means the average particle diameter measured by the dynamic light scattering method.

The particles used in the present invention may be organic particles, inorganic particles, or both. Examples of the composition of inorganic particles that can be used in the present invention include silica, colloidal silica, alumina, ceria, kaolin, talc, mica, calcium carbonate, barium sulfate, carbon black, zeolite, titanium oxide, and various metal oxides. Fine particles are preferred. In particular, inorganic colloidal particles are preferable from the viewpoint of dispersibility in a polyester resin having a hydrophilic functional group, and colloidal silica is particularly preferable. Furthermore, colloidal silica in which -SiOH groups and -OH ^- ions are present on the surface of colloidal silica, an electric double layer is formed in a negatively charged state, and is dispersed and stable in the solvent by electrostatic repulsion between colloidal silica. It is preferable that -SiOH groups and -OH colloidal silica surface ^- ion present, the electric double layer is formed at the charged state negatively, as the colloidal silicas dispersed stably in a solvent by the electrostatic repulsion between the colloidal silica, “Snowtex” (registered trademark) series manufactured by Nissan Chemical Industries, Ltd. and “Cataloid” series manufactured by JGC Catalysts & Chemicals Co., Ltd. are preferably used.

  As a composition of the organic particle which can be used for this invention, the particle | grains which use acrylic acid, styrene resin, thermosetting resin, silicone, an imide compound etc. as a structural component are mentioned, for example. Particles (so-called internal particles) that are precipitated by a catalyst or the like added during the polyester polymerization reaction are also preferably used. In particular, styrene / acrylic particles are preferable from the viewpoints of dispersibility in a polyester resin having a hydrophilic functional group and versatility. As the styrene / acrylic particles stably dispersed in the liquid, “Movinyl” (registered trademark) 972 manufactured by Nippon Synthetic Chemical Industry Co., Ltd. is preferably used.

<Formation method of undercoat layer>
The undercoat layer is formed on the substrate by applying the organic binder described above and, if necessary, a coating composition containing an additive or a solvent to the substrate and drying the solvent as necessary. be able to.

  Moreover, it is preferable to use an aqueous solvent as a solvent for the coating composition. A coating composition using an aqueous solvent is sometimes referred to as a coating composition containing an aqueous solvent. By using an aqueous solvent, rapid evaporation of the solvent in the drying step can be suppressed, and not only a uniform undercoat layer can be formed, but also the environmental load is excellent.

  Here, the aqueous solvent is soluble in water such as water or water and alcohols such as methanol, ethanol, isopropyl alcohol and butanol, ketones such as acetone and methyl ethyl ketone, and glycols such as ethylene glycol, diethylene glycol and propylene glycol. A certain organic solvent is mixed in an arbitrary ratio.

  The coating composition can be applied on the substrate by known wet coating methods such as spray coating, dip coating, spin coating, knife coating, kiss coating, gravure coating, slot die coating, roll coating, bar coating, and screen printing. Inkjet printing, pad printing, and other types of printing can be used. Further, a dry coating method may be used. As the dry coating method, physical vapor deposition such as sputtering or vapor deposition, chemical vapor deposition, or the like can be used. Moreover, application | coating may be performed in multiple times and it may combine two different types of application | coating methods. Preferred coating methods are gravure coating, bar coating, and slot die coating, which are wet coatings.

  After the application step, the dispersion medium is removed from the undercoat paint containing the dispersant applied in the drying step. Solvent removal methods include convection hot-air drying where hot air is applied to the substrate, radiant heat drying where the substrate absorbs infrared rays by radiation from an infrared drying device, and heats and heats to dry. It is possible to apply conductive heat drying that is heated and dried by heat conduction. Of these, convection hot air drying is preferred because of its high drying rate.

  In the following, a film having an undercoat layer formed on a substrate may be referred to as an undercoat laminated film.

[Conductive layer]
FIG. 1 shows a conceptual diagram of a cross section of an undercoat laminated film 102 in which an undercoat layer 104 is formed on a substrate 103 and a laminate 101 in which a conductive layer 105 is further laminated. In the present invention, the conductive layer 105 is not particularly limited as long as it includes a carbon nanotube 106 and a carbon nanotube dispersion 109. For example, an enzyme, a viscosity modifier, an emulsifier, and a pH adjuster used as a biosensor. An agent, an ionic conduction aid, a conduction aid, an electrochemical activator, and the like may be included.

[carbon nanotube]
The carbon nanotube used in the present invention is not particularly limited as long as it has a shape obtained by winding one surface of graphite into a cylindrical shape. Single-wall carbon in which one surface of graphite is wound in one layer. Both nanotubes and multi-walled carbon nanotubes wound in multiple layers (three or more layers) can be used. Among them, in particular, carbon in which one-sided graphite is wound in two layers and carbon nanotubes containing 50 or more double-walled carbon nanotubes are included. Nanotubes are preferred because the conductivity and the dispersibility of the carbon nanotubes in the coating dispersion are extremely high. More preferably, 75 or more of 100 are double-walled carbon nanotubes, and most preferably 80 or more of 100 are double-walled carbon nanotubes. It should be noted that the fact that 50 double-walled carbon nanotubes are contained in 100 may indicate that the percentage of double-walled carbon nanotubes is 50%. In addition, the double-walled carbon nanotube is preferable in that the original function such as conductivity is not impaired even if the surface is functionalized by acid treatment or the like.

  For example, the carbon nanotube is manufactured as follows. A powdery catalyst in which iron is supported on magnesia is present in the entire horizontal cross-sectional direction of the reactor in a vertical reactor, and methane is supplied in the vertical direction into the reactor. The carbon nanotubes containing single- to five-layer carbon nanotubes can be obtained by contacting the carbon nanotubes at 200 ° C. to produce carbon nanotubes and then oxidizing the carbon nanotubes. Carbon nanotubes can be manufactured and then subjected to an oxidation treatment to increase the ratio of single to five layers, particularly the ratio of two to five layers. The oxidation treatment is performed, for example, by a nitric acid treatment method. Nitric acid is preferred because it acts as a dopant for the carbon nanotubes. The dopant is a function of giving a surplus electron to the carbon nanotube or taking away the electron to form a hole, thereby generating a freely movable carrier, thereby improving the conductivity of the carbon nanotube. Is. Further, by performing the oxidation treatment, it is possible to increase the number of defects and the number of functional groups in the outer layer of the double-walled carbon nanotube. The nitric acid treatment method is not particularly limited as long as the carbon nanotube of the present invention can be obtained, but is usually performed in an oil bath at 140 ° C. The nitric acid treatment time is not particularly limited, but is preferably in the range of 0.5 to 50 hours.

  As shown in FIG. 2, the reaction activity of the carbon material electrode is particularly high in a portion having a carbon graphite structure defect 201, a Sto-wales defect 202, and a functional group 203 such as an —OH group or ═O. Yes. As shown in FIG. 3, in the double-walled carbon nanotube electrode, defects or functional groups such as —COOH groups and —OH groups are intentionally introduced into the outer layer in the carbon nanotube oxidation process described above, and the inner layer generates defects. There can be no structure. As a result, a carbon material having high conductivity and high electrochemical activity can be obtained.

  Furthermore, in the present invention, the first carbon nanotube with few defects described later and high conductivity is mixed with the second carbon nanotube intentionally introduced with many defects to increase the electrochemical activity. It becomes possible to obtain a conductive layer having higher conductivity and higher electrochemical activity. When the entire conductive layer is 100% by mass, it is preferable that the first carbon nanotubes are contained in an amount of 1.0% by mass or more and the second carbon nanotubes are contained in an amount of 1.0% by mass or more. In order to have activity, it is more preferable that the first carbon nanotube is 10.0% by mass or more and the second carbon nanotube is 2.0% by mass or more, and the first carbon nanotube is 20.0% by mass or more. It is particularly preferable that the second carbon nanotubes are contained in an amount of 4.0% by mass or more.

<First carbon nanotube>
The first carbon nanotube used in the present invention has a maximum peak intensity in the range of 1,560 to 1,600 cm ^{−1 in} the range of 1,560 to 1,600 cm ⁻¹ by resonance Raman scattering measurement, and in the range of 1,310 to 1,350 cm ⁻¹ . When the maximum peak intensity is D, G / D is preferably 30 or more, and more preferably 60 or more from the viewpoint of conductivity.

<Second carbon nanotube>
The second carbon nanotube used in the present invention preferably has the aforementioned G / D of 10 or less, and more preferably 5 or less from the viewpoint of electrochemical activity.

[Carbon nanotube dispersant]
The conductive layer preferably contains a carbon nanotube dispersant (hereinafter also referred to simply as a dispersant) together with the carbon nanotubes.

  As the carbon nanotube dispersant, surfactants, various polymer materials (water-soluble polymer materials, etc.) and the like can be used, and ionic polymer materials are preferable because of high dispersibility. Examples of the ionic polymer material include an anionic polymer material, a cationic polymer material, and an amphoteric polymer material. After the carbon nanotube dispersion liquid is applied to the substrate, the dispersant serves as a binder existing between the carbon nanotubes, for example. When measuring the absolute value of the charge density described later, it is measured by immersing in an aqueous solution that is an electrolytic solution. Since the ionic polymer material has a high affinity with water, the affinity between the hydrophobic carbon nanotube and the aqueous solution can be increased, the electrode reaction area can be increased, and the electrochemical activity can be improved. . Any kind of ionic polymer material can be used as long as it has a high affinity with water, has a high ability to disperse carbon nanotubes, can stably coexist with a redox substance, and can maintain dispersibility. For example, a substance containing carboxymethyl cellulose, a salt of polystyrene sulfonic acid, or the like can be used. Among them, a substance containing carboxymethyl cellulose is preferable, and among the substances containing carboxymethyl cellulose, carboxymethyl cellulose and its salt (sodium salt, ammonium salt, etc.) can efficiently disperse carbon nanotubes in the carbon nanotube dispersion liquid. (Hereinafter, carboxymethyl cellulose and its salt may be referred to as carboxymethyl cellulose salt and polystyrene sulfonic acid salt as polystyrene sulfonate).

  In the present invention, when carboxymethyl cellulose salt or polystyrene sulfonate is used, examples of the cationic substance constituting the salt include alkali metal cations such as lithium, sodium and potassium, and alkaline earth such as calcium, magnesium and barium. Metal cation, ammonium ion, or monoamineamine, diethanolamine, triethanolamine, morpholine, ethylamine, butylamine, coconut oil amine, tallow amine, ethylenediamine, hexamethylenediamine, diethylenetriamine, polyethyleneimine and other onium ions, Alternatively, these polyethylene oxide adducts can be used, but are not limited thereto.

[Method for producing conductive layer]
In the present invention, the method for producing the conductive layer is not particularly limited, but the conductive layer is preferably produced through an application step of applying the carbon nanotube dispersion liquid to the substrate and a drying step of removing the dispersion medium thereafter.

  In the present invention, the method for applying the dispersion on the substrate or the undercoat layer is not particularly limited. Known application methods such as spray coating, dip coating, spin coating, knife coating, kiss coating, gravure coating, slot die coating, bar coating, roll coating, screen printing, inkjet printing, pad printing, other types of printing, etc. Available. Moreover, application | coating may be performed in multiple times and it may combine two different types of application | coating methods. The most preferred application methods are gravure coating, bar coating, and die coating.

  After the coating step, the dispersion medium is removed from the carbon nanotube dispersion containing the dispersant applied in the drying step. Solvent removal methods include convection hot-air drying where hot air is applied to the substrate, radiant heat drying where the substrate absorbs infrared rays by radiation from an infrared drying device, and heats and heats to dry. It is possible to apply conductive heat drying that is heated and dried by heat conduction. Of these, convection hot air drying is preferred because of its high drying rate.

[Carbon nanotube dispersion]
Although the preparation method of the carbon nanotube dispersion liquid used in this invention is not specifically limited, For example, it can carry out in the following procedures. Since the treatment time at the time of dispersion can be shortened, once a dispersion liquid containing carbon nanotubes in a concentration range of 0.003 to 0.30 mass% in the dispersion medium is prepared, the dispersion liquid is diluted with a solvent, and thereby a predetermined amount is obtained. The concentration is preferably used. In the present invention, the mass ratio of the dispersant to the carbon nanotube (dispersant / carbon nanotube) is preferably 10 or less. Within such a preferable range, it is easy to uniformly disperse, but there is little influence of the decrease in conductivity. The mass ratio of the dispersant to the carbon nanotube is more preferably 0.2 to 9.0, still more preferably 0.4 to 6.0, and the mass ratio of the dispersant to the carbon nanotube is 0.6 to 2.5 is particularly preferable because high dispersibility and conductivity can be obtained. In the present invention, in order to mix the first carbon nanotube and the second carbon nanotube having appropriate G / D, both are prepared as separate carbon nanotube dispersions, and then both the carbon nanotube dispersions are mixed. Thus, a carbon nanotube dispersion may be prepared.

  In the present invention, the carbon nanotube dispersion may contain various additives. Examples of the additive may include a redox compound, an enzyme, a viscosity modifier, an emulsifier, a pH adjuster, an ion conduction aid, a conduction aid, and an electrochemical activator.

  As a dispersion means at the time of preparation, a carbon nanotube, a dispersant and an additive are mixed and dispersed in a dispersion medium, which is commonly used for coating production (for example, a ball mill, a bead mill, a sand mill, a roll mill, a homogenizer, an ultrasonic homogenizer, a high-pressure homogenizer, A sonic device, an attritor, a resolver, a paint shaker, etc.). Moreover, you may disperse | distribute in steps, combining these some mixing dispersers. Among these, the dispersion method using an ultrasonic device is preferable because the dispersibility of the carbon nanotubes in the resulting coating dispersion liquid is good and the control of G / D is easy.

[solvent]
The solvent used in the present invention is preferably water from the viewpoints that the dispersant can be easily dissolved and that the treatment of the waste liquid is easy.

[Charge transfer resistivity]
FIG. 4 shows a general configuration of a blood glucose level sensor as an example of an electrode type sensor. A reagent layer is provided on the conductive layer 105 to form the reagent conductive layer 401. A reagent conductive layer 401 that generates an oxidation reaction that extracts electrons from glucose and serves as a working electrode of an electrochemical reaction; a working electrode wiring 402 that transmits a current generated by the oxidation reaction generated in the reagent conductive layer 401 to a measurement unit (not shown); A counter electrode 403 that generates a reduction reaction with respect to the oxidation current generated in the reagent conductive layer 401 and maintains the balance of the electrochemical system, a counter electrode wiring 404 that supplies electrons from a measurement unit (not shown) to the counter electrode, and a base material that supports the above 103.

  The reagent conductive layer 401 is generally composed of an enzyme that takes electrons from glucose, a redox substance that receives electrons from these enzymes and transmits electrons to the conductive layer in the reagent conductive layer, and a conductive layer that causes an electrode reaction as a working electrode.

  The principle of blood glucose measurement is as follows.

  When blood to be measured is dropped on the reagent conductive layer and the counter electrode, glucose in the blood is deprived of electrons by an enzyme (such as glucose dehydrogenase) that specifically acts only on glucose. The deprived electrons cannot directly move to the conductive layer in the reagent conductive layer, and transfer the electrons to the redox body. The redox body to which the electrons are transferred moves to the conductive layer in the reagent conductive layer, and transfers the electrons to the conductive layer.

  Through this series of reactions, electrons are transferred to the conductive layer. Since the current value generated at this time increases or decreases according to the glucose concentration, the glucose concentration in the blood can be measured. The working electrode wiring 402 and the counter electrode wiring 404 play a role of transmitting a current generated at the working electrode and the counter electrode to the measurement unit.

As described above, the redox material causes an electrode reaction at the working electrode, which is a conductive layer, and the electrode reactivity is one of the important factors for highly accurate measurement. However, in order to increase the electrode reactivity, it is not preferable in terms of cost to make the conductive layer to be an electrode excessive. In addition, when the working electrode made of the conductive layer has an excessive area, the pain of blood collection is reduced, so that it is difficult to reduce the size of the electrode reaction part so that the amount of blood necessary for measurement can be reduced. Further, laser patterning is one of the patterning methods such as a working electrode and a counter electrode provided for causing an electrode reaction. However, when the conductive layer has an excessive thickness, the laser processability may deteriorate. It is not preferable that the conductive layer has an excessive volume also in terms of narrowing the degree of freedom in designing the sensor. That is, a conductive layer having a smaller volume and high electrode reactivity is preferable. In the present invention, the charge transfer resistivity of the conductive layer is used as an indicator of a small volume and high electrode reactivity. The required charge transfer resistivity is preferably 2.0 × 10 ⁻⁹ Ωcm ³ or less from the viewpoints of electrode reactivity, cost, and design freedom of the sensor.

[Electric resistivity]
As described above, the working electrode wiring 402 and the counter electrode wiring 404 play a role of transmitting a current generated in the working electrode and the counter electrode to the measurement unit, and therefore need a certain degree of conductivity. In addition, when an electrode reaction occurs, a voltage is applied between the working electrode and the counter electrode. However, when the working electrode wiring 402 and the counter electrode wiring 404 have low conductivity, a voltage drop occurs, so that the amount of current obtained is small. There is a case. In addition, a conductive layer having a small volume and high conductivity is preferable for the same reason as described above. In the present invention, electrical resistivity is used as an indicator of small volume and high conductivity. The required electrical resistivity is preferably 5.0 × 10 ⁻⁴ Ωcm or less from the viewpoints of suppression of voltage drop, cost, and sensor design flexibility.

[Usage]
Since the laminate of the present invention has both high electrochemical activity and conductivity even in a small volume, it can be preferably used for an electrode for an electrochemical device for measuring current. Moreover, the laminated body of this invention can be used suitably for an electrode type sensor. Furthermore, the laminate of the present invention can be particularly preferably used for a blood glucose level sensor.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by these Examples.

[Measurement method]
The measurement method used in this example is shown below. Unless otherwise specified, when obtaining a numerical value from a measured value, the number of measurements was set to twice, and the average value was adopted as the numerical value.

<Charge transfer resistivity>
Impedance spectroscopy was performed using the conductive layer of each sample as a working electrode, and the charge transfer resistance of potassium ferrocyanide in the electrolyte was measured. Charge transfer resistance represents electrochemical activity.

As an electrolytic solution, an aqueous solution prepared to contain potassium ferrocyanide at a concentration of 5 mmol / l, potassium ferricyanide at a concentration of 5 mmol / l, and potassium chloride at a concentration of 0.5 mol / l was used. An Ag / AgCl electrode (manufactured by BAS: RE-1B aqueous reference electrode) was used as the reference electrode, and a Pt electrode (manufactured by BAS: Pt counter electrode 5.7 cm) was used as the counter electrode. The working electrode is prepared by cutting each sample into 10 mm × 20 mm and further bonding the insulating tape with a 3 mm diameter circular hole on the conductive layer to make the working electrode area constant 0.071 cm ^2. Used. An FRA board was added to a potentiostat (Hokuto Denko Co., Ltd .: HZ-7000), and impedance spectroscopy was performed. The measurement potential was a natural potential, the potential fluctuation was 10 mV, and the frequency was 1 Hz to 10 kHz. The Cole-Cole plot of the impedance spectroscopy obtained in this way was analyzed with analysis software (Hokuto Denko Co., Ltd .: EIS Version 1.0.23) to derive the charge transfer resistance. The equivalent circuit used at that time is the same as that shown in FIG. As the fitting method, the Levenberg-Marquard method was used. Search conditions are as follows.
・ Calculation point generation: Mesh fitting calculation: once per search ・ Number of search censoring: 10,000
Absolute tolerance: 1.0 × 10 ⁻¹⁵
Relative tolerance: 1.0 × 10 ⁻¹⁵
・ Maximum number of repetitions: 100
-Difference: forward difference-difference step width: 0.0001.

The charge transfer resistance was calculated by multiplying the charge transfer resistance derived as described above by the working electrode area (0.071 cm ² ) and further by multiplying the thickness of the conductive layer described later.

<Thickness of conductive layer>
The conductive layer is removed by laser etching to form a step, and the step portion is scanned within a range of 80 μm × 80 μm by AFM (manufactured by Bruker: Dimension Icon) to obtain a three-dimensional profile of height, In the three-dimensional profile of the height, the difference (B−A) between the mode value (A) of the height of the substrate region and the mode value (B) of the height of the conductive layer portion is defined as the thickness of the conductive layer. Evaluated.

<Electric resistivity>
The probe was brought into close contact with the central portion on the conductive layer side of the laminate having a size of 5 cm × 10 cm, and the surface resistance value of the conductive layer was measured at room temperature by the four-terminal method. The used apparatus is a resistivity meter MCP-T360 manufactured by Dia Instruments, and the probe used is a 4-probe probe MCP-TPO3P manufactured by Dia Instruments. The electrical resistivity was calculated by multiplying the measured surface resistance value of the conductive layer by the thickness of the conductive layer.

<G / D>
A sample for G / D measurement is prepared by applying a carbon nanotube dispersion liquid described later on a base material that has been subjected to a corona treatment described later to improve hydrophilicity, in a bar coat number 10 and then dried at 100 ° C. for 1 minute. Produced. Each sample was cut into a size of 20 mm × 20 mm, and then excited with a laser Raman microscope (manufactured by Nanophoton Co., Ltd .: RAMANtouch) with an excitation wavelength of 532 nm, an output of 1.5 mW, an exposure time of 300 seconds, a grating of 600 gr / mm, and a slit width of 50 μm. The Raman spectrum was obtained by measuring under the following conditions. The maximum peak intensity in the range of 1,560 to 1,600 cm ⁻¹ of each Raman spectrum obtained is G, the maximum peak intensity in the range of 1,310 to 1,350 cm ⁻¹ is D, and G G / D was derived by dividing D from.

[Sample preparation method]
The method for preparing the sample used in this example is shown below.

<Base material>
A polyethylene terephthalate film (“Lumirror” (registered trademark) E20 manufactured by Toray Industries, Inc., thickness 250 μm, whiteness 91.7%) was used as a base material for each example and comparative example.

<Corona treatment>
Using a corona surface modification evaluation apparatus (TEC-4AX manufactured by Kasuga Electric Co., Ltd.), corona treatment was performed with an E value of 100 W · min / m ² and a discharge electrode-ground plate discharge gap interval of 1 mm.

<Undercoat solution>
An organic binder containing a polyester resin having a hydrophilic functional group and an acrylic resin having a hydrophilic functional group (A647-GEX manufactured by Takamatsu Yushi Co., Ltd., solid content concentration: 20% by mass, water solvent) and colloidal silica (Nissan Chemical Industries ( Co., Ltd. “Snowtex” (registered trademark) ST-O, particle size 10 nm to 15 nm, solid content concentration 20% by mass) is mixed and diluted with water and isopropanol (hereinafter, IPA). The ratio with IPA was adjusted to 7: 3 by mass ratio, the solid content concentration of the resin and silica combined was 2.5 mass%, and the mass ratio of resin to silica was 9: 1.

<Preparation of carbon nanotube synthesis catalyst>
About 24.6 g of iron (III) ammonium citrate (manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in 6.2 kg of ion-exchanged water. About 1,000 g of magnesium oxide (MJ-30 manufactured by Iwatani Corporation) was added to this solution, and after vigorously stirring for 60 minutes with a stirrer, the suspension was introduced into a 10 L autoclave container. At this time, 0.5 kg of ion exchange water was used as a washing solution. In a sealed state, it was heated to 160 ° C. and held for 6 hours. Thereafter, the autoclave container was allowed to cool, the slurry-like cloudy substance was taken out from the container, excess water was filtered off by suction filtration, and a small amount of water contained in the filtered material was dried by heating in a 120 ° C. drier. The obtained solid content was collected on a sieve and the particle size in the range of 10 to 20 mesh was recovered while being finely divided in a mortar. The granular catalyst body shown on the left was introduced into an electric furnace and heated at 600 ° C. for 3 hours in the atmosphere. The bulk density was 0.32 g / mL. Further, when the filtrate was analyzed by an energy dispersive X-ray analyzer (EDX), iron was not detected. From this, it was confirmed that the added iron (III) ammonium citrate was supported on the entire amount of magnesium oxide. Furthermore, from the EDX analysis result of the catalyst body, the iron content contained in the catalyst body was 0.39% by mass.

<Synthesis of carbon nanotubes>
Carbon nanotubes were synthesized using the catalyst. A catalyst layer was prepared by taking 132 g of the solid catalyst and introducing it onto a quartz sintered plate at the center of the reactor installed in the vertical direction. While heating the catalyst layer until the temperature in the reaction tube reaches about 860 ° C., nitrogen gas is supplied from the bottom of the reactor toward the top of the reactor at 16.5 L / min so as to pass through the catalyst layer. Circulated. Thereafter, while supplying nitrogen gas, methane gas was further introduced at 0.78 L / min for 60 minutes and aeration was performed so as to pass through the catalyst body layer to cause a reaction. The introduction of methane gas was stopped, and the quartz reaction tube was cooled to room temperature while supplying nitrogen gas at 16.5 L / min to obtain a carbon nanotube composition with a catalyst. 129 g of this catalyst-attached carbon nanotube composition was stirred in 4.8 mL of a 4.8N hydrochloric acid aqueous solution for 1 hour to dissolve the catalyst metal iron and the carrier MgO. The obtained black suspension was filtered, and the filtered product was again put into 400 mL of a 4.8N hydrochloric acid aqueous solution, treated with MgO, and collected by filtration. This operation was repeated three times to obtain a carbon nanotube from which the catalyst was removed.

<Production of hydrolyzed carboxymethyl cellulose>
10 mass% sodium carboxymethylcellulose (Daiichi Kogyo Seiyaku Co., Ltd., Cellogen 5A (weight average molecular weight: 80,000, molecular weight distribution (Mw / Mn): 1.6, degree of etherification: 0.7)) aqueous solution 500 g was added to a three-necked flask and adjusted to pH 2 using primary sulfuric acid (Kishida Chemical Co., Ltd.). This container was transferred to an oil bath heated to 120 ° C., and subjected to a hydrolysis reaction for 9 hours with stirring under heating and reflux. After allowing the three-necked flask to cool, the reaction was stopped by adjusting the pH to 10 using a 28 mass% aqueous ammonia solution (manufactured by Kishida Chemical Co., Ltd.) to obtain a hydrolyzed sodium carboxymethylcellulose solution. The weight average molecular weight of hydrolyzed sodium carboxymethylcellulose was calculated by comparing with a calibration curve with polyethylene glycol using a gel permeation chromatography method. As a result, the weight average molecular weight was about 35,000, and the molecular weight distribution (Mw / Mn) was 1.5.

<Preparation of carbon nanotube dispersion>
The manufacturing method of the carbon nanotube dispersion liquid used for each Example and the comparative example is shown below.

(1) Carbon nanotube dispersion A
The synthesized carbon nanotubes were added to concentrated nitric acid (first grade assay 60-61% by mass, manufactured by Wako Pure Chemical Industries, Ltd.) having a mass of about 300 times. Thereafter, the mixture was heated to reflux with stirring in an oil bath at about 140 ° C. for 24 hours. After heating to reflux, a nitric acid solution containing carbon nanotubes was diluted twice with ion exchange water and suction filtered. After washing with ion-exchanged water until the suspension of the filtered material became neutral, a carbon nanotube wet cake containing carbon nanotubes and water was stored. When the average outer diameter of the carbon nanotube was observed with a high-resolution transmission electron microscope, it was 1.7 nm. The ratio of the double-walled carbon nanotubes is 90% by mass, the combustion peak temperature is 725 ° C., and the carbon nanotube concentration of the carbon nanotube wet cake obtained from the mass after drying by heating and blowing at 200 ° C. for 2 hours in the heating and blowing oven is It was 3.4% by mass.

  0.5 g of the carbon nanotube wet cake diluted with ion exchange water so as to be 3.0% by mass, and 4.5 g of the hydrolyzed sodium carboxymethylcellulose solution diluted with ion exchange water so as to be 0.5% by mass. Then, 1.5 g of an aqueous solution of ammonium carbonate (manufactured by Wako Pure Chemical Industries, Ltd.) diluted with ion-exchanged water so as to be 2.0% by mass and 3.5 g of water are mixed, and 10.0 g of carbon is mixed. A nanotube mixture was prepared. The mixture was dispersed for 6 minutes using an ultrasonic homogenizer (VCX-130, manufactured by Ieda Trading Co., Ltd.) under the conditions of 75% output and 30 second period (30 seconds output and 30 second output stop). The dispersion treatment was carried out under cooling so that the liquid temperature was 10 ° C. or lower. The obtained dispersion was diluted with ion-exchanged water so that the concentration of carbon nanotubes was 0.075% by mass to obtain a carbon nanotube dispersion A. The G / D of the conductive layer prepared from the dispersion was 80.

(2) Carbon nanotube dispersion B
A carbon nanotube dispersion liquid B was obtained in the same manner as in the preparation of the carbon nanotube dispersion liquid A except that the dispersion treatment time by the ultrasonic homogenizer was changed to 30 minutes instead of 6 minutes. The G / D of the conductive layer prepared from the dispersion was 44.

(4) Carbon nanotube dispersion C
A carbon nanotube dispersion C was obtained in the same manner as in the preparation of the carbon nanotube dispersion A except that the dispersion treatment time by the ultrasonic homogenizer was 1,440 minutes instead of 6 minutes. The G / D of the conductive layer prepared from the dispersion was 2.

(5) Carbon nanotube dispersion D
Single-walled carbon nanotubes (OCSiAl, TUBALL) 0.3 g, 9.0 g of the hydrolyzed sodium carboxymethylcellulose solution diluted with ion-exchanged water so as to be 5.0% by mass, and 2.0% by mass. Thus, 30 g of an aqueous solution of ammonium carbonate (manufactured by Wako Pure Chemical Industries, Ltd.) diluted with ion-exchanged water and 60.7 g of water were mixed to prepare 100 g of a carbon nanotube mixed solution. 400 g of zirconia beads having a diameter of 1.0 mm (Traceram beads, manufactured by Toray Industries, Inc.) are added to the mixed solution, and the number of revolutions is set to 4 with a ball mill (Fritsch, planetary ball mill P-6) at a rotation speed of 400 rpm. After stirring for a period of time, the zirconia beads were removed using a 50 mesh filter (Nylon Mesh 50, manufactured by Sinky Corporation) and a rotating / revolving mixer (NRE-250, manufactured by Sinky Corporation). A 30% by mass single-walled carbon nanotube slurry was prepared. 5.0 g of the single-walled carbon nanotube slurry and 5.0 g of ion-exchanged water were mixed to prepare a 10.0 g carbon nanotube mixed solution. The mixed solution was subjected to dispersion treatment under ice-cooling for 6 minutes under the conditions of 75% output and 30-second cycle by the ultrasonic homogenizer. The carbon nanotube dispersion liquid D was obtained by adjusting the liquid temperature during dispersion to 10 ° C. or lower. The G / D of the conductive layer prepared from the dispersion was 47.

(5) Carbon nanotube dispersion E
0.75 g of multi-walled carbon nanotube (manufactured by Sakai Kogyo Co., Ltd., NC7000, carbon nanotube in which 50 or more carbon nanotubes of three or more layers are contained in 100) and 25 g of ion-exchanged water are mixed, and blender (Osaka A 3.0 mass% multi-walled carbon nanotube wet cake was prepared by using a Warming J-SPEC Blender 7010JBB manufactured by Chemical Co., Ltd. and stirring for 3 minutes at a rotational speed of 22,500 rpm.

  In the preparation of the carbon nanotube dispersion B, the same method except that 0.5 g of the multi-walled carbon nanotube wet cake is used instead of the carbon nanotube wet cake diluted with ion-exchanged water so as to be 3.0% by mass. Preparation, dispersion, and dilution were performed to obtain a carbon nanotube dispersion E.

<Undercoat laminated film production example>
An undercoat layer was produced on the substrate by the method shown below.

  The base material was subjected to the corona treatment to improve the hydrophilicity of the base material. On the base material, the undercoat liquid was applied with a bar coat number 6 and then dried at 125 ° C. for 1 minute using a hot air oven to prepare an undercoat laminated film.

Example 1
A dispersion obtained by mixing and stirring the carbon nanotube dispersion liquid A and the carbon nanotube dispersion liquid C at a mass ratio of 9: 1 on the undercoat laminated film was applied with a bar coat number 8 and then at 100 ° C. for 1 minute. It was made to dry and the laminated body which has a conductive layer was produced.

(Example 2)
A dispersion obtained by mixing and stirring the carbon nanotube dispersion liquid A and the carbon nanotube dispersion liquid C at a mass ratio of 3: 1 on the undercoat laminated film was applied with a bar coat number 8 and then at 100 ° C. for 1 minute. It was made to dry and the laminated body which has a conductive layer was produced.

(Example 3)
A dispersion obtained by mixing and stirring the carbon nanotube dispersion liquid A and the carbon nanotube dispersion liquid C at a mass ratio of 1: 1 is applied to the undercoat laminated film with a bar coat number 8 and then at 100 ° C. for 1 minute. It was made to dry and the laminated body which has a conductive layer was produced.

(Comparative Example 1)
The carbon nanotube dispersion liquid A was applied on the undercoat laminated film at a bar coat number of 8, and then dried at 100 ° C. for 1 minute to produce a laminate having a conductive layer.

(Comparative Example 2)
The carbon nanotube dispersion liquid B was applied on the undercoat laminated film at a bar coat number of 8, and then dried at 100 ° C. for 1 minute to produce a laminate having a conductive layer.

(Comparative Example 3)
The carbon nanotube dispersion C was applied on the undercoat laminated film with a bar coat number of 8, and then dried at 100 ° C. for 1 minute to produce a laminate having a conductive layer.

(Comparative Example 4)
The carbon nanotube dispersion liquid D was applied on the undercoat laminated film at a bar coat number of 8, and then dried at 100 ° C. for 1 minute to produce a laminate having a conductive layer.

(Comparative Example 5)
The carbon nanotube dispersion liquid E was applied on the undercoat laminated film with a bar coat number 8 and then dried at 100 ° C. for 1 minute to produce a laminated body having a conductive layer. Laminated body having each conductive layer Table 1 shows the results of the evaluations performed for.

  The present invention can be suitably used, for example, as an electrode for measuring current. In particular, it can be suitably used as an electrode for an electrochemical device or a blood glucose level sensor.

101: laminate 102: undercoat laminated film 103: base material 104: undercoat 105: conductive layer 106: carbon nanotube 107: first carbon nanotube 108: second carbon nanotube 109: carbon nanotube dispersant 201: carbon Defect 202 of graphite structure: Sto-wales defect 203: Functional group 401 such as —OH group and ═O: Reagent conductive layer 402: Working electrode wiring 403: Counter electrode 404: Counter electrode wiring 501: Charge transfer resistance 502: Warburg impedance 503: CPE (constant phase element)
504: Circuit resistance

Claims (6)

A laminate having a carbon nanotube and a conductive layer containing a carbon nanotube dispersant on a substrate, potassium ferrocyanide at a concentration of 5 mmol / l, potassium ferricyanide at a concentration of 5 mmol / l, and a concentration of 0.5 mol / l A laminate having a charge transfer resistivity at a natural potential of 2.0 × 10 ⁻⁹ Ωcm ³ or less based on a silver / silver chloride electrode when immersed in an aqueous solution containing potassium chloride. The laminate according to claim 1, wherein the electric resistivity of the conductive layer is 5.0 × 10 ⁻⁴ Ωcm or less. The following 1st carbon nanotube is 1.0 mass% or more and the 2nd carbon nanotube is 1.0 mass% or more when the said whole conductive layer is 100 mass%, or 1 characterized by the above-mentioned. 2. The laminate according to 2.
First carbon nanotube: by resonance Raman scattering measurement, the maximum peak intensity in the range of 1,560~1,600cm ^-1 G, a maximum peak intensity in the range of 1,310～1,350Cm ^-1 A second carbon nanotube in which G / D is 30 or more when D is D: G / D is 10 or less   The said carbon nanotube contains a double-walled carbon nanotube, The laminated body in any one of Claims 1-3 characterized by the above-mentioned.   The laminate according to any one of claims 1 to 4, wherein the carbon nanotube dispersant contains carboxymethylcellulose.   An electrode type sensor comprising the laminate according to any one of claims 1 to 5.

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